While it is true that you can hardly be forced to love someone, and that the opposite is also true, there is a point where it just becomes... forced, in a story, ironically enough. Ruka honestly might have ended up with Kazuya far sooner than the story has gone, if not for Deus Ex Machina/chance events/etc, such as seeing a blonde girl walk by through the window and immediately thinking "Oh, hey, Mami".
Ruka is the sort of person you'd just naturally fall in love with over time, at least in Kazuya's place, as he is shown to react to her actions as is. While he does remark how he can't just come to like her, you'd be surprised what one or two weeks of spending time with someone would do. It's honestly rather sad that, despite it being the deal, he never truly gave her a chance -instead he'd just put up with her like some needy dog while he chased after Mizuhara, which is a damn shame, all things considered. Even if he didn't end up falling in love, it'd have at least made for more compelling reading than what we actually did get, what with however many chapters of nothing we got, all of which got capped off with plot suddenly enabling fast travel just to slap down Ruka's confession in front of Kazuya's family.
Similarly, where the hell is Mami? She may not really be a love intrest, but she is still a vital spice that this rather flavorless series could really benefit from. As it stands now, she'll only reappear at or near the absolute end, revealing to everyone that "she was a rental girlfriend, all along!", but ...like, that would not only suck ass, but it would also be a discredit to her. Her appearances, while brief, tended to add some serious, tangible tension to whatever scene was going on. It was as if she walked in with a gun and gave everyone an offer they couldn't refuse -hell, we don't even know her backstory, or at the very least the specific reason she is the way she is.
Sumi, she's best girl. Not best waifu, but best girl, largely because she would totally come to accept that she wasn't chosen by the MC and remain a good friend of his (even if only after a brief period of time to get over it). Her appearances are something of an opposite to Mami's, but instead of a gun and a vaguely threatening 'offer', she comes with soothing presence and just the sort of emotional support Kazuya needs in order to stop being a massive bitch for at least the next four chapters. Six if we're lucky. There should be more of her, honestly.
Kibe gets too little screentime, he's Kazuya's main bro. Sure, he's not a main character, but he appears once every, what, 50 chapters? Rather, he has a presence once every 50 chapters, it's nonsensical. His is a voice of reason, though he, due to not being privy to the truth of the situation, often misunderstands what Kazuya is actually doing. This could be interesting, like how it was during the beach chapters, but, nah, let's just bring him up once so that Mami can know where he works. Except out of all of Kazuya's friends, Kibe is likely the least willing to divulge that information, as he was the only one to actually see past her facade (if only partly) and realize what she was really doing back on the beach. If anyone would distrust Mami, it'd be him.
Lastly, the fish. For obvious reasons.
